BEIJING (Reuters) - Chinese judicial authorities are processing a corruption case against a one-time mistress of the country's disgraced top security boss, a state-run Beijing newspaper reported on Thursday.

Citing anonymous sources, the paper said Li Xiaomei reaped more than 30 million yuan ($4.6 million) by illicitly obtaining and reselling distribution rights for natural gas.

Jiang Jiemin, once the top regulator of state-owned assets and a close acolyte of former security tzar Zhou Yongkang, aided Li in obtaining rights to sell the natural gas, the paper said.

Neither Li nor China's top anti-corruption body, the Central Commission for Discipline Inspection, could be reached for comment.

China's biggest oil company, China National Petroleum Corporation (CNPC), was a power base for Zhou.

Jiang himself was felled in President Xi Jinping's corruption crackdown, along with many other Zhou allies. Jiang is also a former head of CNPC, the parent of PetroChina Co. Ltd..

Zhou was jailed for life in June after a secret trial.

He was the most senior Chinese official to be caught up in a graft scandal since the Communists took power in 1949 and the highest-ranking to be prosecuted since the fall of the Gang of Four in 1976 after the Cultural Revolution.

The official Xinhua news agency reported at the time that Zhou had abused his power to help relatives, mistresses and friends reap "huge profits", resulting in losses of state-owned assets.

Xi has warned that rampant corruption threatens the survival of the ruling party. Scores of top officials in the party, the government, the military and state-owned companies have been brought down in a sweeping anti-graft campaign.